This investigation concerns the roles of atmospheric pollutants--individually and in combination--in the etiology and pathogenesis of chronic obstructive lung disease through the medium of experimental models of emphysema in the rat. The disease is induced by long-term exposure to subacute concentrations of NO2, O3, and their combination. Studies include respiratory physiology, hematology, gross and microscopic pathology, electron microscopy, cellular dynamics (renewal), and biochemistry. Pathogenesis involves mild injury to respiratory epithelium with replacement of ciliated bronchiolar cells and Type 1 cells by nonciliated and Type 2 cells, respectively, by injury mainly to the terminal and respiratory bronchioles, alveolar ducts, and proximal alveoli. Eventually, the lungs develop large residual volumes, small airway obstruction, and a relative increase in compliance. Alveoli become enlarged and reduced in number. Biochemical studies include the reactions of NO2 with tissue, vitamins E and A, connective tissue elements, surfactant, enzymes in alveolar macrophages, and ATP and 2,3:DPG in the polycythemic erythrocytes.